A distributed antenna system (“DAS”) can be used to provide wireless communications coverage in a variety of environments, particularly in large structures such as office buildings, convention halls, airports, stadiums, and the like. A DAS can include one or more master units or other head-end units that are communicatively coupled to one or more base stations. A DAS can also include multiple remote units that are communicatively coupled to each master unit. The remote units, each of which can include one or more transceivers and antennas, can be distributed across a coverage area. The remote units can transmit the downlink signals to mobile phones or other terminal devices within coverage areas serviced by the remote units.
A master unit of a DAS may combine uplink transmissions received from several remote units into a composite signal. Combining uplink transmissions from different remote units communicating with the same terminal device can boost the power of weak uplink signals received by one or more remote units. The composite uplink signal may be provided to a base station that communicates with the DAS.
A master unit may combine uplink transmissions regardless of whether the uplink transmissions includes uplink signals from terminal devices or includes only uplink noise. Combining uplink signals regardless of whether uplink signals from terminal devices are present may present disadvantages. For example, uplink transmissions from one or more remote units may include noise on one or more channels, even if no uplink signal has been received by the remote units. Combining the uplink transmissions from each of the remote units to generate a composite uplink signal can combine the received noise in each uplink channel. If some of the uplink transmissions includes noise but does not include an uplink signal, indiscriminately combining uplink transmissions may unnecessarily increase the noise floor for the composite uplink signal and limit the number of remote units used in the DAS.